JP2017031891A - Piston for internal combustion engine, internal combustion engine, and design method of piston for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piston for an internal combustion engine which promotes a mixture of fuel spays and intake air in a cavity by utilizing a swirl, and can avoid the generation of suit, HC, CO or the like caused by incomplete combustion by suppressing the formation of a fuel over-rich region by the interference of the fuel sprays, and provide the internal combustion engine, and a design method of the piston for the internal combustion engine.SOLUTION: A region of a cavity 10 is divided into sectioned regions Di at respective injection holes 31 of a fuel injection nozzle 30, a shelf part 14 having a recess at an upper side portion of an external periphery of an external peripheral wall 11 of the cavity 10 is arranged at the inside of the sectioned regions Di, a boundary portion with the sectioned region Di+1 which adjoins the sectioned region Di is formed into a shape having no recessed shelf part 14, and a shape of the shelf part 14 is formed so that a gouged amount of the recess becomes large at an upstream side of a swirl, and gradually becomes small at a downstream side of the swirl with respect to a direction of the swirl.SELECTED DRAWING: Figure 1

Description

  The present invention, in an internal combustion engine such as a diesel engine, promotes mixing of fuel spray and intake air in a cavity (combustion chamber) and suppresses the generation of a fuel-rich region due to interference between adjacent fuel sprays. The present invention relates to a piston for an internal combustion engine that can avoid generation of soot, HC, CO, and the like due to incomplete combustion, an internal combustion engine, and a piston design method for the internal combustion engine.

  In a piston for an internal combustion engine such as a diesel engine, a concave portion called a cavity is provided at the top (crown surface: piston top) of the piston, and fuel is injected from a fuel injection nozzle provided facing the center of the cavity. The injected fuel spray is mixed with the intake air inside the cavity to burn the fuel. In this combustion, there is generation of soot, HC, CO, etc. due to incomplete combustion. The phenomenon is as follows. As shown in FIG. 8, in the cavity 10X provided at the top 2 of the piston 1X, as shown in FIG. 9, the fuel spray F is made to flow into the swirl S after colliding with the outer peripheral wall 11 of the cavity 10X. The fuel spray Fs flowed to the swirl S exists on the downstream side of the swirl, and as shown in FIG. 10, the fuel sprays F1 and F2 injected from the adjacent injection holes 31 overlap in the cavity 10X and interfere with each other. Arise.

  When the fuel sprays F1 and F2 interfere with each other, there is a risk that an over-concentrated region Ro that is deficient in oxygen with respect to the fuel may be formed, and soot, HC, CO, and the like may be generated. This is a finding obtained from observation results of combustion in an internal combustion engine. In order to avoid these phenomena and improve the combustion efficiency, various contrivances have been made to the shape of the cavity.

  For example, in order to suppress the formation of a fuel-rich region due to fuel spray injected from the injector toward the cavity spreading in the circumferential direction along the wall surface of the cavity and adjacent sprays interfering with each other, Combustion chamber structure of an internal combustion engine having a cavity in which a plurality of sprays of fuel injected from an injector disposed at the top at a top collide with each other at intervals in the circumferential direction, and the spray collides with the wall surface of the cavity. A combustion chamber structure for an internal combustion engine that suppresses interference between adjacent sprays by providing a plurality of guide protrusions along the inner and outer directions of the cavity and spreading the sprays along the wall surface in the circumferential direction of the cavity. It has been proposed (see, for example, Patent Document 1).

  However, it has been found that when the soot is deposited in the recesses, the effect of the guide protrusions may be diminished or the guide protrusions may be destroyed by thermal stress.

  In other words, the structure for preventing spray diffusion is a structure that is easily damaged by thermal stress, so there is room for improvement that it is not suitable for use in areas with high loads, and the cross-sectional shape of the piston cavity Since there is no significant change in the circumferential direction and the structure of the swirl (transverse vortex: swirl) flow is not used to promote the mixing of spray and intake air, there is also room for improvement in this aspect. Obtained.

In this connection, the direct injection corresponding to the fuel injection nozzle that atomizes the fuel with the momentum injected from the injection hole because the combustion efficiency of the squish area was increased with a simple structure while maintaining the volume of the combustion chamber as much as possible. The piston of a diesel-type internal combustion engine is independent of the outer periphery of the combustion chamber individually corresponding to the combustion chamber recessed at the top and the diffusion range of the fuel spray injected from the plurality of nozzle holes of the fuel injection nozzle. A piston has been proposed in which the cross-sectional shape of the recess along the radial direction of the piston is provided in accordance with the distribution of the fuel concentration of the fuel spray that varies depending on the circumferential position with respect to the center of the piston ( For example, see Patent Document 1).

  However, in this configuration, since the depression is provided at the top of the piston independently of the space of the combustion chamber, it is effective in improving the combustion of fuel spray in the squish area beyond the outer peripheral edge of the combustion chamber. However, there is a problem that it is not directly useful for improving the combustion in the center of the combustion chamber.

JP 2011-174388 A JP 2010-112350 A

  The present invention has been made in view of the above, and an object of the present invention is to promote mixing of fuel spray and intake air in a cavity by using a swirl in an internal combustion engine such as a diesel engine. Of an internal combustion engine, an internal combustion engine, and a piston for an internal combustion engine that can prevent generation of soot, HC, CO, etc. due to incomplete combustion by suppressing generation of a fuel rich region due to interference between fuel sprays It is to provide a method.

  In order to achieve the above object, a piston for an internal combustion engine according to the present invention comprises a cavity provided in a concave shape at the top of the piston, and a fuel injection nozzle provided in a cylinder head facing the center of the cavity. An internal combustion engine piston for an internal combustion engine for swirling intake air, wherein the region of the cavity is divided into divided regions for each injection hole of the fuel injection nozzle, and the peripheral wall surface of the cavity is inside the divided region The upper part of the outer periphery of the partition is provided with a shelf having a recess, and is formed in a shape having no shelf at the boundary with the partition area adjacent to the partition area, and the swirl upstream side of the partition area with respect to the direction of the swirl Then, the first transition part that transitions from the shape without the shelf part to the shape that forms the shelf part extending to the outer periphery side, and the outer periphery side of the depression gradually to the center of the partition region A first dent that increases the amount of sag, a maximum dent that maximizes the amount of sag toward the outer periphery of the dent at the center of the partition region, and the dent gradually from the center of the partition region to the swirl downstream side. A second depression that reduces the amount of turning to the outer peripheral side of the rim, and a second transition portion that transitions from the shape of the shelf to the shape without the shelf on the downstream side of the swirl of the partition region , Formed so as to be continuous with the shape of the swirl uppermost stream side of the adjacent partition region, and further, the depressions in the order of the first transition part, the second transition part, the second depression part, and the first depression part. The amount of change with respect to the circumferential direction in the amount of turning to the outer peripheral side is made small.

  According to this configuration, each fuel spray has a structure in which the cross-sectional area of the cavity changes in the circumferential direction of the cavity of the piston and is devised so that the intake air and the fuel spray in the partition region are mixed. It is possible to sufficiently mix the intake air and the fuel spray, and the generation of soot, HC, CO and the like can be suppressed. This partition area is set corresponding to the nozzle hole, that is, changes depending on the number of nozzle holes.

  Further, since the interference between adjacent sprays is prevented by eliminating the overlap between adjacent sprays, it is possible to suppress the generation of a fuel rich region due to the interference between adjacent fuel sprays. , HC and CO can be avoided. In addition, since mixing of intake air and fuel spray is favorably promoted, soot and CO can be reduced also in this aspect.

  Therefore, in an internal combustion engine such as a diesel engine, the swirl is used to promote the mixing of the fuel spray and the intake air in the cavity, while suppressing the occurrence of a fuel rich region due to the interference between adjacent fuel sprays, Generation of soot, HC, CO, etc. due to incomplete combustion can be avoided.

  In the piston for the internal combustion engine, the mouth portion of the corner portion with the top portion of the piston is formed to protrude toward the piston central axis at a portion of the second recess portion where the shelf portion is located. In other words, after the injected fuel spray collides with the outer peripheral wall of the cavity, it is structured to project the mouth of the cavity so as to mix with the intake air at the center of the cavity while being swirled. This facilitates mixing of the fuel spray with the intake air at the center of the cavity in accordance with the swirl flow.

  In addition, due to the structure of this mouth portion, when the piston exceeds the compression top dead center and enters the expansion stroke, the flow that flows from the cavity to the cylinder is called a reverse squish flow. And it becomes possible to promote mixing of intake air.

  In order to achieve the above object, an internal combustion engine of the present invention is configured to include the above-described piston for the internal combustion engine, and can achieve the same effects as the above fuel injection device.

  A method for designing a piston for an internal combustion engine according to the present invention for achieving the above object is provided in a cylinder head facing a cavity formed in a concave shape at the top of the piston and a central portion of the cavity. In a method for designing a piston for an internal combustion engine for an internal combustion engine that has a fuel injection nozzle and swirls intake air, the fuel spray injected from each nozzle hole of the fuel injection nozzle flows by a predetermined swirl. The first step of measuring or calculating the range to be measured, the mixture distribution of injected fuel spray and intake air is measured, and the oxygen amount in the intake air mixed with the amount of fuel spray is less than the equivalent ratio 1 A second step of measuring or calculating a region and the region of the cavity are partitioned so that the region of each injection hole of the fuel injection nozzle includes the region having an equivalent ratio of less than 1 3 and steps, a method characterized by a fourth step of determining the shape of the cavity for each of the divided area.

  In the above-described method for designing a piston for an internal combustion engine, in the fourth step, in the direction in which fuel is injected from the nozzle hole, a mixing distance until the fuel spray collides with the outer peripheral wall of the cavity is gained. Therefore, the outer peripheral wall of the cavity is arranged far from the central axis of the piston, and on the downstream side of the swirl, the fuel spray collides with the outer peripheral wall of the cavity and then mixes with the intake air inside the cavity while being swirled by the swirl. In order to prevent the fuel spray from colliding with the outer peripheral wall of the cavity on the upstream side of the swirl, so that there is no interference with the adjacent fuel spray, The outer peripheral wall of the cavity is arranged close to the piston central axis side, and the sectional shape of the cavity in a plane including the piston central axis Is rotated along the circumferential direction around the piston central axis along the flow of the swirl, and the cavity continuously extends so as to return to the original state after the cavity expands to the outside along with the rotation. Create a shape.

  According to these internal combustion engine piston design methods, the same operational effects as the above-described internal combustion engine piston can be achieved.

  According to the piston for the internal combustion engine, the internal combustion engine, and the piston design method for the internal combustion engine according to the present invention, in the internal combustion engine such as the diesel engine, the swirl is used to promote the mixing of the fuel spray and the intake air in the cavity. In addition, generation of soot, HC, CO, and the like due to incomplete combustion can be avoided by suppressing generation of a fuel rich region due to interference between adjacent fuel sprays.

It is a sectional side view of the piston which shows typically the structure of the cavity of the piston for internal combustion engines of an embodiment concerning the present invention. It is a figure for demonstrating the 1st step in the design method of the piston for internal combustion engines of embodiment which concerns on this invention, and is a figure which shows typically the flow of the fuel spray by a swirl in a cavity. It is a figure for demonstrating the 2nd step and 3rd step in the design method of the piston for internal combustion engines of embodiment which concerns on this invention, and is a figure which shows typically the area | region where the equivalent ratio is less than 1 in a cavity. It is a figure for demonstrating the 4th step in the design method of the piston for internal combustion engines of embodiment which concerns on this invention, and is a figure which shows typically the division area in a cavity, and the position of each cross section. It is a figure which shows typically the cross-sectional shape in the piston for internal combustion engines of embodiment which concerns on this invention. It is a perspective view which shows three-dimensionally the cross-sectional shape in the piston for internal combustion engines of embodiment which concerns on this invention. It is a figure which shows typically the state of the adjacent fuel spray in the piston for internal combustion engines of embodiment which concerns on this invention. It is a sectional side view of the piston which shows typically the structure of the cavity of the piston for internal combustion engines of a prior art. It is a figure which shows typically the flow of the fuel spray by a swirl in the cavity of the piston for internal combustion engines of a prior art. It is a figure which shows typically the state of the overlap of the adjacent fuel spray in the cavity of the piston for internal combustion engines of a prior art.

  Hereinafter, a piston for an internal combustion engine, an internal combustion engine, and a method for designing a piston for an internal combustion engine according to embodiments of the present invention will be described with reference to the drawings. The internal combustion engine of the embodiment according to the present invention is configured to include the piston for the internal combustion engine of the embodiment according to the present invention, and has the same operational effects as the operational effects exhibited by the piston for the internal combustion engine described later. Can play.

  First, a method for designing a piston for an internal combustion engine according to an embodiment of the present invention will be described. As shown in FIG. 1, the piston design method for the internal combustion engine includes a cavity 10 provided in a concave shape at the top 2 of the piston 1 and a cylinder head (not shown) facing the center of the cavity 10. This is a method of designing a piston for an internal combustion engine for an internal combustion engine that has a fuel injection nozzle 30 provided on the internal combustion engine and swirls intake air.

  As shown in FIG. 1, the cavity 10 includes an outer peripheral wall 11, a bottom portion 12, an outer edge portion 13, a mouth portion (projecting portion) 13 a, a shelf portion 14, a recess 15, and a mouth portion (projecting portion) 16 of the shelf portion 14. And so on.

  This piston designing method for an internal combustion engine has first to fourth steps. In the first step, as shown in FIG. 2, each of the fuel injection nozzles 30 is set by a swirl S set in advance. A range Rs in which the fuel spray F injected from the injection hole 31 flows by colliding with the virtual outer peripheral wall 11X is measured or calculated. Since this virtual outer peripheral wall 11X is for obtaining the range Rs through which the fuel spray F flows, it may be of an appropriate shape, for example, a cavity shape having an annular outer peripheral wall of the prior art may be used. it can.

  Further, in the second step, as shown in FIG. 3, the mixture distribution of the injected fuel spray F and the intake air is measured, and the amount of oxygen in the intake air mixed with the amount of the fuel spray F becomes redundant. A region R1 having an equivalence ratio of less than 1 is measured or calculated.

  Then, in the third step, as shown in FIG. 3, the equivalence ratio in the partition region Di for each injection hole 31 of the fuel injection nozzle 30 is defined by the straight line Li and the straight line Li + 1 extending from the center of the cavity 10. It partitions so that less than 1 area | region R1 may be included. In the next fourth step, as shown in FIGS. 4 to 6, the shape of the cavity 10 is determined for each partition region Di. This partition area Di changes corresponding to the number of nozzle holes 31, in other words, the number of nozzle holes 31. That is, there are as many partitioned areas Di as the number of nozzle holes 31.

  That is, for the purpose of setting the shape of the cavity (combustion chamber) 10 so as to reduce the interference between the adjacent fuel sprays F, the range in which the fuel sprays F are flowed by a preset swirl S is measured or fluid analysis Calculate by using a program, etc., and measure the equivalent ratio (reciprocal of excess air ratio = weight of oxygen required for complete combustion / weight of oxygen in the actual mixture) using the LAS method (laser absorption scattering method) , A region R1 having an equivalence ratio of less than 1, in other words, a region R1 in which oxygen is surplus is a range divided in the circumferential direction of the cavity 10 so as to be arranged for each partition region Di ejected from each nozzle hole 31. The partition region Di is determined, and the cross-sectional shape (S1 to S7) of the cavity 10 for each partition region Di determined in the region where the fuel spray F injected from each nozzle hole 31 is generated is determined.

  Based on the swirl S set in advance, the partition area Di is set so that the equivalence ratio is less than 1 in the circumferential direction of the cavity 10 as viewed from above, and the sectional shape (S1) of the cavity 10 is set for each partition area Di. To S7). When setting the cross-sectional shape (S1 to S7) of the cavity 10, the portion S4 where the injected fuel spray F directly collides is set as far as possible from the injection hole 31, and the sprays overlap on the virtual outer peripheral wall 11X. A wall-like shape is set at a location (S1, S7) where the equivalence ratio exceeds 1 and oxygen shortage occurs or is calculated, and adjacent injected fuel sprays F1, F2 Avoid overlapping. Therefore, the cross-sectional shapes (S1, S7) at both ends of each partition area Di reduce the distance from the piston central axis C in the radial direction of the cavity 10 so as not to interfere with the fuel sprays F1, F2 in the adjacent areas.

  In the fourth step, in the direction (cross section S4) in which the fuel spray F is injected from the nozzle hole 31, in order to earn a mixing distance until the fuel spray F collides with the outer peripheral wall 11 of the cavity 10, The outer peripheral wall 11 of the cavity 10 is arranged far from the piston central axis C, and on the downstream side of the swirl (sections S5 and S6), the fuel spray F collides with the outer peripheral wall 11 of the cavity 10 and then flows through the swirl S. The mouth portion 13a of the cavity 10 is projected so as to push in the fuel spray F so as to be mixed with the intake air inside the fuel, and the fuel spray F is on the outer peripheral wall 11 of the cavity 10 on the swirl upstream side (sections S2 and S3). 6, the outer peripheral wall 11 of the cavity 10 is arranged close to the piston central axis C side so that there is no interference with the adjacent fuel spray F, as shown in FIG. When the sectional shape (S1 to S7) of the cavity 10 in the plane including the piston central axis C is rotated along the circumferential direction around the piston central axis C along the flow of the swirl S, this rotation Accordingly, the shape of the cavity 10 is created by continuing the cavity 10 so as to return to the original state after spreading outward. That is, the shape of the cavity 10 is created by continuously extending the cross-sectional shape (S1 to S7) of the cavity 10 in a plane including the piston center axis C so as to spread in the circumferential direction around the piston center axis C.

  That is, the cross-sectional shape (S1 to S7) obtained by cutting the cavity 10 along the plane including the piston central axis C changes in the radial direction according to the direction of the swirl S in accordance with the swirl S that is the flow of intake air in the cavity 10. Concerning the change of the cross-sectional shape (S1 to S7) of the cavity 10, the mouth portion 13a of the location (S4) where the fuel spray F directly collides is the farthest location from the injection hole 31, and the first step and the first step As a result obtained in two steps, a wall-like shape is set in a portion (S1, S7) that overlaps with the adjacent fuel spray F and has an equivalent ratio exceeding 1. Further, as the fuel spray F flows through the swirl S, the mouth portion 13a is pushed out toward the center C so as to push in the fuel F so that the fuel spray F mixes with the intake air on the center C side of the cavity 10. .

  Next, a piston (hereinafter referred to as a piston) 1 for an internal combustion engine according to an embodiment of the present invention will be described. As shown in FIGS. 1 to 6, the piston 1 is provided in a cavity 10 provided in a concave shape at the top 2 of the piston 1 and in a cylinder head (not shown) facing the central portion of the cavity 10. This is a piston for an internal combustion engine for an internal combustion engine that has a fuel injection nozzle 30 and swirls intake air.

  In this piston 1, the area of the cavity 10 is divided into divided areas Di for each injection hole 31 of the fuel injection nozzle 30, and the upper peripheral portion of the outer peripheral wall 11 of the cavity 10 has a recess 15 inside the divided area Di. A portion 14 is provided.

  At the same time, in the boundary portion with the partition area Di + 1 adjacent to the partition area Di, the shelf section 14 having the depression 15 is not formed, and with respect to the direction of the swirl S, on the swirl uppermost stream side (S1) of the partition area Di. The 1st transition part (S1-S2) which provides the hollow 15 which extends in the outer peripheral side from the shape without the shelf part 14 and transfers to the shape which formed the shelf part 14 is provided.

  Moreover, the 1st hollow part (S2-S4) which enlarges the turning amount to the outer peripheral side of the hollow 15 gradually to the center (S4) of the division area Di, and the outer peripheral side of the depression 15 in the center (S4) of the division area Di A maximum depression (S4) that maximizes the amount of twisting is provided.

  Furthermore, the second depression (S4 to S6) that gradually reduces the amount of turning of the depression 15 from the center (S4) of the partition area Di toward the downstream side of the swirl, and the most downstream side of the swirl (S7) of the partition area Di. ) Is formed with a second transition portion (S6 to S7) that transitions from a shape of the shelf portion 14 having the recess 15 to a shape without the shelf portion 14 having the recess 15, and the uppermost swirl of the adjacent partition region Di + 1 It is formed so as to be continuous with the side shape.

  In addition, the outer peripheral side of the recess 15 in the order of the first transition portion (S1 to S2), the second transition portion (S2 to S4), the second recess portion (S4 to S6), and the first recess portion (S6 to S7). The amount of change with respect to the circumferential direction is reduced.

  That is, regarding the shape of the cavity (combustion chamber) 10, the cross-sectional shape (S 1 to S 7) extending in the radial direction from the piston central axis C for each fuel spray F injected from the injection hole 31 of the fuel injection nozzle 30 is circumferential. A cavity shape is created by superimposing them in a fan shape.

  And the largest hollow part (S4) which is a location where the fuel spray F collides directly is made as far as possible in order to earn the mixing distance until the fuel spray F collides. Further, in the second depression (S4 to S6), after the fuel spray F collides with the outer peripheral wall 11 of the cavity 10, the cavity 10 is mixed with the intake air in the central portion C of the cavity 10 while being swirled by the swirl S. The mouth portion 13a is shaped to protrude toward the piston central axis C so that the mouth portion 13a pushes in the fuel spray F.

  Thereby, in the part (S4 to S6) where the mixing of the fuel spray F and the intake air is desired to be promoted as much as possible, the mixing time is long, and the mixing region becomes large so that the injected fuel spray F collides with the cavity 10. The outer peripheral wall 11 is formed far away.

  On the other hand, in the first depression (S2 to S4) on the swirl upstream side in the direction opposite to the direction of the swirl flow, adjacent to the fuel spray F adjacent to each other on both sides of the partition region Di. A barrier is provided to gradually reduce the distance from the piston central axis C in the radial direction of the cavity 10 so as not to interfere with the injected fuel spray F so as not to overlap with the adjacent injected fuel spray F. Make the shape to be formed.

  In this cavity 10, the outer edge portion 13 which is a line inside the top portion 2 of the piston 1 is injected with fuel from the injection hole 31 when viewed from above the piston center axis C as shown in FIGS. 4 and 6. It is not line-symmetric with respect to the direction of, but is non-line-symmetric.

  According to this configuration, the structure in which the cross-sectional area of the cavity 10 changes in the circumferential direction of the cavity 10 of the piston 1 for each fuel spray F, and the intake air in the partition region Di and the fuel spray F are mixed. Therefore, the intake air in the cavity 10 and the fuel spray F can be sufficiently mixed, and generation of soot, HC, CO, and the like can be suppressed.

  Further, as shown in a region Rx in FIG. 7, the overlap between the injected adjacent fuel sprays F1 and F2 is eliminated so that there is no interference, so the fuel due to the interference between the adjacent fuel sprays F1 and F2 It is possible to suppress the generation of an excessively concentrated region, thereby avoiding the generation of soot, HC, and CO due to incomplete combustion. Further, since mixing of the intake air and the fuel spray F is favorably promoted, soot and CO can be reduced also in this aspect.

  Moreover, in the site | part (S4-S6) with the shelf part 14 of a 2nd hollow part, the base part 13a of the corner | angular part with the top part 2 of the piston 1 and the base part 16 of the shelf part 14 are on the piston central axis C side. Protruding and forming. In other words, after the injected fuel spray F collides with the outer peripheral wall 11 of the cavity 10 and then flows in the swirl S, the mouth portion 13a of the cavity 10 is mixed with the intake air on the center side of the cavity 10. , And the mouth portion 16 of the shelf portion 14 is projected. Accordingly, the fuel spray F is easily mixed with the intake air on the center side of the cavity 10 in accordance with the flow of the swirl S.

  In addition, by the structure of the mouth portions 13a and 16, the reverse squish flow that flows from the cavity 10 to the cylinder when the piston 1 exceeds the compression top dead center and enters the expansion stroke can be utilized. Mixing can be promoted.

  Therefore, according to the piston for the internal combustion engine, the internal combustion engine, and the piston design method for the internal combustion engine having the above-described configuration, in the internal combustion engine such as a diesel engine, the fuel spray F in the cavity 10 is utilized using the swirl S. As a result, the generation of soot, HC, CO, etc. due to incomplete combustion can be avoided by suppressing the generation of a fuel rich region due to interference between adjacent fuel sprays F.

1, 1X Piston for internal combustion engine
2 Piston top part 10, 10X Cavity 11 Cavity outer peripheral wall 11X Virtual outer peripheral wall 12 Cavity bottom part 13 Cavity outer edge part 13a Cavity mouth part (extrusion part)
14 Shelf part 15 Dimple 16 Shelf's mouth part (protruding part)
30 Fuel injection nozzle 31 Injection hole C Center part of cavity (piston central axis)
Di partition region F Fuel spray Li, Li + 1 Straight line Rs extending from the center of the cavity R1 Range in which the fuel spray collides with the virtual outer peripheral wall R1 Equivalence ratio less than 1 region S Swirl S1 to S7 Cross sectional shape of the cavity

Claims (5)

In a piston for an internal combustion engine for an internal combustion engine having a cavity provided in a concave shape at the top of the piston and a fuel injection nozzle provided in a cylinder head so as to face the central portion of the cavity and for swirling intake air ,
Dividing the region of the cavity into compartments for each nozzle hole of the fuel injection nozzle;
While providing a shelf having a depression on the outer peripheral upper side portion of the outer peripheral wall of the cavity inside the partition region, and forming a shape without the shelf at the boundary portion with the partition region adjacent to the partition region,
Regarding the direction of the swirl,
On the uppermost swirl side of the partition region, a first transition portion that transitions from a shape without the shelf portion to a shape that forms the shelf portion extending to the outer periphery side, and gradually toward the outer periphery side of the depression to the center of the partition region A first dent that increases the amount of sag, a maximum dent that maximizes the amount of sag toward the outer periphery of the dent at the center of the partition region, and the dent gradually from the center of the partition region to the swirl downstream side. A second depression that reduces the amount of turning to the outer peripheral side of the rim, and a second transition portion that transitions from the shape of the shelf to the shape without the shelf on the downstream side of the swirl of the partition region , Formed to be continuous with the shape of the swirl upstream side of the adjacent partition area,
Furthermore, the amount of change with respect to the circumferential direction in the amount of turning toward the outer peripheral side of the recess is reduced in the order of the first transition portion, the second transition portion, the second recess portion, and the first recess portion. A piston for an internal combustion engine.   2. The piston for an internal combustion engine according to claim 1, wherein a mouth portion of a corner portion with respect to a top portion of the piston is protruded toward a piston central axis side at a portion of the second recess portion where the shelf portion is provided.   An internal combustion engine comprising the piston for an internal combustion engine according to claim 1 or 2. A piston for an internal combustion engine for an internal combustion engine having a cavity provided in a concave shape at the top of the piston and a fuel injection nozzle provided in a cylinder head facing the central portion of the cavity and for swirling intake air In the design method,
A first step of measuring or calculating a range in which the fuel spray injected from each nozzle hole of the fuel injection nozzle flows by a swirl set in advance;
A second step of measuring a mixture distribution of the injected fuel spray and the intake air, and measuring or calculating a region less than an equivalence ratio of 1 where the amount of oxygen in the intake air mixed with respect to the amount of the fuel spray is excessive;
A third step of dividing the region of the cavity so as to include the region of less than 1 in the partition region for each nozzle hole of the fuel injection nozzle;
And a fourth step of determining a shape of the cavity for each of the partition regions. A method for designing a piston for an internal combustion engine. In the fourth step,
In the direction in which the fuel is injected from the nozzle hole, the outer peripheral wall of the cavity is arranged far from the piston central axis in order to increase the mixing distance until the fuel spray collides with the outer peripheral wall of the cavity.
On the downstream side of the swirl, after the fuel spray collides with the outer peripheral wall of the cavity, the shape of the cavity is pushed out so as to mix with the intake air inside the cavity while flowing by the swirl. age,
On the swirl upstream side, after the fuel spray collides with the outer peripheral wall of the cavity, the outer peripheral wall of the cavity is arranged close to the piston central axis side so that there is no interference with the adjacent fuel spray,
When the cross-sectional shape of the cavity in a plane including the piston central axis is rotated along the circumferential direction around the piston central axis along the flow of the swirl, the cavity is exposed to the outside along with the rotation. The method for designing a piston for an internal combustion engine according to claim 4, wherein the shape of the cavity is continuously formed so as to return to the original state after spreading.

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